### STS configuration can fail if STS endpoints are unspecified

#### Affected Versions

- 1.19.0

#### Issue

When configuring an sts endpoint in the AWS Secrets engine, when no sts_endpoint is set, the engine will return
an error stating that the number of endpoints and regions do not match:

```
{"errors":["number of regions does not match number of endpoints"]}
```

#### Workaround

Explicitly set the default endpoint and region when configuring sts:

```
{
...
  sts_region = "us-east-1"
  sts_endpoint = "https://sts.amazonaws.com"
...
}
```
